Silicone hydrogel contact lenses are typically made by co-polymerizing one or more silicone-containing monomers with one or more hydrophilic-containing monomers within a contact lens mold that shapes the front and back surfaces of the contact lens. After polymerization, the lens is removed from the mold and processed to hydrate and remove unreactive materials from the lens. Lenses may be subjected to further processes to increase the hydrophilicity of the surface of the contact lens. Typically the front (i.e. anterior) and back (i.e. posterior) surfaces of a contact lens have the same material properties. However, the two surfaces are exposed to very different environments. The front surface of a lens is exposed to the air-tear interface, where water from within the hydrogel lens is susceptible to evaporation. The back surface of the lens is exposed to the eye-cornea interface. It has been proposed that contact lens dehydration is induced by water evaporation at the anterior surface followed by water transport from the posterior to the anterior lens surface (see Little and Bruce, ICLC 22 (1995) 148-155), which can lead to thinning of post-lens tear film and in turn may lead to corneal epithelial cell damage, as evidenced by a fluorescein eye stain test. Contact lens discomfort is commonly associated with corneal staining.
New silicone hydrogel contact lenses that are less susceptible to dehydration, have reduced incidence of corneal staining, and are more comfortable for the wearer are desired.
Background publications include U.S. Pat. Nos. 6,551,531, 8,979,261, U.S. Publ. No. 2016/0159019, U.S. Publ. No. 2008/02950534, and U.S. Pat. No. 9,156,214.